1. Field of the Invention
The present invention relates to a deposition process for planar lightwave devices and particularly to an improved apparatus and method for depositing thin films onto a substrate.
2. Technical Background
A key step in the manufacturing of planar optical components is the deposition of thin films onto a substrate. Planar optical components require that the deposited doped thin glass films have uniform properties when used as planar waveguides for optical components used, for example, in the telecommunication industry.
The soot/glass deposition rate by the flame hydrolysis deposition (FHD) process is thermophoretically dominated and, it was discovered, is adversely influenced by variations in the substrate temperature. Typically, a silica, si, sapphire or other wafer substrate is held in a vacuum chuck which is rotated and a line-flame burner translated with respect to the chuck to provide a uniform coating of doped glass material onto the substrate. It was discovered, however, that the uniformity of the thickness of a film coating utilizing such a process varied over the surface of the resultant wafer-shaped coated substrate as did the index of refraction despite the rotation as well as the translation in X-Y directions of the substrate relative to the flame during the FHD process. This discovery of a pattern of thickness variations and index of refraction variations lead to experimental testing of the temperature of a chuck exposed to a line-flame translated across the chuck and the resultant discovery that significant temperature variations occur during the exposure of the chuck, and a wafer substrate attached to the chuck, to a line-flame burner. As a result of the discovery of the pattern of thickness variations and index of refraction variations and the resultant correlation of such variations with variations in the temperature of the chuck, the source of the problem of film thickness and index of refraction variations was discovered.